In line with miniaturization of patterns of LSI elements, there is a demand for a new exposure technology. A method for exposure to X-rays, electron beams or ion beams used in recent years uses a thin stencil mask with openings corresponding to patterns of their respective LSI elements.
According to a conventional electron beam exposure apparatus, a resist, which is applied to a silicon wafer and photosensitive to electron beams, is irradiated with electron beams through an exposure mask. At this time, the resist in an area corresponding to an opening provided in an exposure mask causes a photoreaction due to electron beams, which have passed through the opening.
“Photoreaction” is a term indicating a physical or chemical change in a matter that occurs when light beams or X-rays act on the matter, and in the present Specification, it is also used as a term indicating a physical or chemical change in a matter that occurs when electron beams or ion beams act on the matter. That is, the term “photoreaction” in the present Specification indicates a physical or chemical change in a matter that occurs when radiation acts on the matter.
FIG. 26 is a cross-sectional view of a conventional electron beam exposure mask. As shown in FIG. 26, an electron beam exposure mask 51 is constructed of a frame 20 made of glass, etc. a silicon plate 11 provided on the under surface of the frame 20 and a stencil mask 14 provided on the under surface of the silicon plate 11. The stencil mask 14 is formed of a silicon plate coated with SiC or diamond, etc. and provided with patterning openings 14a to form resist patterns. Furthermore, the electron beam exposure mask 51 is provided with a large opening 20a, which penetrates the frame 20 and silicon plate 11 and exposes the area of the upper surface of the stencil mask 14 in which the patterning openings 14a are formed.
FIG. 27 is a cross-sectional view of the X-ray exposure mask 51 used for a conventional X-ray exposure apparatus. As shown in FIG. 27, an X-ray exposure mask 52 is constructed of a frame 20 made of glass, etc., a silicon plate 11 provided on the under surface of the frame 20, a membrane 12 provided on the under surface of the silicon plate 11 and an X-ray shielding metal film 13 provided on the under surface of the membrane 12. The membrane 12 is formed of SiC or diamond, etc. and the X-ray shielding metal film 13 is provided with patterning openings 13a that penetrate the X-ray shielding metal film 13 to form resist patterns. Furthermore, the X-ray exposure mask 52 is provided with a large opening 20a, which penetrates the frame 20 and silicon plate 11 and exposes the area of the upper surface of the membrane 12 located above the area in which the patterning openings 13a of the X-ray shielding metal film 13 are formed.
In the case where a resist 62 is irradiated with electron beams using the conventional electron beam exposure mask 51, if an acceleration voltage for electron beams is small, it is not possible to cause a photoreaction of the resist in the area irradiated with electron beams completely. That is, the surface of the resist of the area irradiated with electron beams causes a photoreaction, but it is difficult to expose the entire resist in the depth direction of the area irradiated with electron beams. To initiate the photoreaction over the entire resist in the film thickness direction of the area irradiated with electron beams requires the acceleration voltage of electron beams to be increased.
However, the energy of accelerated electrons increases as the acceleration voltage increases. When electrons with such high energy collide with the stencil mask 14 of the exposure mask 51, the stencil mask 14 generates heat and expands. This deforms the stencil mask 14. This causes a problem such as preventing the resist from being subject to a photoreaction according to the patterning openings 14a provided on the stencil mask 14.
The same applies to a case where an X-ray photoresist is exposed to X-rays using the conventional X-ray exposure mask 52. When irradiated with strong X-rays such as synchrotron radiation (hereinafter referred to as “SOR light”), the membrane 12 and X-ray shielding metal film 13 are deformed by expansion as in the case of heat generation with electron beams.